num x

The x-coordinate of is display object relative to the local coordinates of the parent DisplayObjectContainer.

If the object is inside a DisplayObjectContainer that has transformations, it is in the local coordinate system of the enclosing DisplayObjectContainer.

Source 

@override
num get x => _x;
void x=(num value)

Source 

@override
set x(num value) {
  if (value is num) _x = value;
  _transformationMatrixRefresh = true;
}